/**
 * Created by Veezilrab on 11/17/2015.
 */
define(['./module', 'THREE'], function (services, THREE) {
    'use strict';

    services.service('Scene', [function(){
        var Scene = function(){
            this.container = null;
            this.edges = {};
            this.projector = new THREE.Projector();

            //setup renderer
            this.threeRenderer = new THREE.WebGLRenderer();
            this.threeRenderer.setClearColor(0xFFFFFF);
            this.threeRenderer.setSize(this.containerWidth, this.containerHeight);

            this.scene = new THREE.Scene();

            //create camera, position it, add to scene
            this.camera = new THREE.PerspectiveCamera(70, this.containerWidth / this.containerHeight, 1, 1000);
            this.camera.position.set(0, 0, 6);
            this.camera.lookAt(this.scene.position);
            this.scene.add(this.camera);

            window.addEventListener('resize', this.onWindowResize.bind(this), false);
        };

        Scene.prototype = {
            constructor: Scene,

            setContainer: function(elem){
                this.container = elem; //keep in mind this is an angular element https://docs.angularjs.org/api/ng/function/angular.element
                this.getContainerSize();

                //get container offset (this is used in getMouseCoords)
                var el = this.container[0];
                for(var lx=0, ly=0; el != null; lx += el.offsetLeft, ly += el.offsetTop, el = el.offsetParent);
                this.containerOffset =  {x: lx?lx:0, y: ly?ly:0};

                //append renderer to container
                this.container.append(this.threeRenderer.domElement);

                this.onWindowResize();
            },

            getContainerSize: function(){
                this.containerWidth = this.container[0].innerWidth || this.container[0].clientWidth;
                this.containerHeight = this.container[0].innerHeight || this.container[0].clientHeight;
            },

            onWindowResize: function() {
                if(this.container === null){return;}

                this.getContainerSize();

                this.camera.aspect = this.containerWidth / this.containerHeight;
                this.camera.updateProjectionMatrix();

                this.threeRenderer.setSize( this.containerWidth, this.containerHeight );

                //calculate edges of screen (this info can be handy for positioning things)
                var vFOV = this.camera.fov * Math.PI / 180; // convert fov to radians
                var visibleH = 2 * Math.tan( vFOV / 2 ) * this.camera.position.z;
                var visibleW = visibleH * this.camera.aspect;

                this.edges = {
                    left: -visibleW/2,
                    right: visibleW/2,
                    top: visibleH/2,
                    bottom: -visibleH/2,
                };
            },

            getMouseCoords: function(event){
                var x = event.clientX - this.containerOffset.x,
                    y = event.clientY - this.containerOffset.y;

                var mouse = new THREE.Vector3();
                mouse.x = (x / this.containerWidth) * 2 - 1;
                mouse.y = -(y / this.containerHeight) * 2 + 1;
                mouse.z = 0.5;

                this.projector.unprojectVector(mouse, this.camera);
                var dir = mouse.sub(this.camera.position).normalize();
                var distance = -this.camera.position.z / dir.z;
                var pos = this.camera.position.clone().add(dir.multiplyScalar(distance));

                return new b2Vec2(pos.x, pos.y);
            },

            render: function(){
                this.threeRenderer.render(this.scene, this.camera);
            },

            reset: function(){
                this.camera.position.set(0, 0, 6);
                this.onWindowResize();
            }
        };

        return new Scene;
    }]);
});/**
 * @author mrdoob / http://mrdoob.com/
 * @author supereggbert / http://www.paulbrunt.co.uk/
 * @author julianwa / https://github.com/julianwa
 */

define(['THREE'], function(THREE) {
    THREE.RenderableObject = function () {

        this.id = 0;

        this.object = null;
        this.z = 0;
        this.renderOrder = 0;

    };

//

    THREE.RenderableFace = function () {

        this.id = 0;

        this.v1 = new THREE.RenderableVertex();
        this.v2 = new THREE.RenderableVertex();
        this.v3 = new THREE.RenderableVertex();

        this.normalModel = new THREE.Vector3();

        this.vertexNormalsModel = [new THREE.Vector3(), new THREE.Vector3(), new THREE.Vector3()];
        this.vertexNormalsLength = 0;

        this.color = new THREE.Color();
        this.material = null;
        this.uvs = [new THREE.Vector2(), new THREE.Vector2(), new THREE.Vector2()];

        this.z = 0;
        this.renderOrder = 0;

    };

//

    THREE.RenderableVertex = function () {

        this.position = new THREE.Vector3();
        this.positionWorld = new THREE.Vector3();
        this.positionScreen = new THREE.Vector4();

        this.visible = true;

    };

    THREE.RenderableVertex.prototype.copy = function (vertex) {

        this.positionWorld.copy(vertex.positionWorld);
        this.positionScreen.copy(vertex.positionScreen);

    };

//

    THREE.RenderableLine = function () {

        this.id = 0;

        this.v1 = new THREE.RenderableVertex();
        this.v2 = new THREE.RenderableVertex();

        this.vertexColors = [new THREE.Color(), new THREE.Color()];
        this.material = null;

        this.z = 0;
        this.renderOrder = 0;

    };

//

    THREE.RenderableSprite = function () {

        this.id = 0;

        this.object = null;

        this.x = 0;
        this.y = 0;
        this.z = 0;

        this.rotation = 0;
        this.scale = new THREE.Vector2();

        this.material = null;
        this.renderOrder = 0;

    };

//

    THREE.Projector = function () {

        var _object, _objectCount, _objectPool = [], _objectPoolLength = 0,
            _vertex, _vertexCount, _vertexPool = [], _vertexPoolLength = 0,
            _face, _faceCount, _facePool = [], _facePoolLength = 0,
            _line, _lineCount, _linePool = [], _linePoolLength = 0,
            _sprite, _spriteCount, _spritePool = [], _spritePoolLength = 0,

            _renderData = {objects: [], lights: [], elements: []},

            _vector3 = new THREE.Vector3(),
            _vector4 = new THREE.Vector4(),

            _clipBox = new THREE.Box3(new THREE.Vector3(-1, -1, -1), new THREE.Vector3(1, 1, 1)),
            _boundingBox = new THREE.Box3(),
            _points3 = new Array(3),
            _points4 = new Array(4),

            _viewMatrix = new THREE.Matrix4(),
            _viewProjectionMatrix = new THREE.Matrix4(),

            _modelMatrix,
            _modelViewProjectionMatrix = new THREE.Matrix4(),

            _normalMatrix = new THREE.Matrix3(),

            _frustum = new THREE.Frustum(),

            _clippedVertex1PositionScreen = new THREE.Vector4(),
            _clippedVertex2PositionScreen = new THREE.Vector4();

        //

        this.projectVector = function (vector, camera) {

            console.warn('THREE.Projector: .projectVector() is now vector.project().');
            vector.project(camera);

        };

        this.unprojectVector = function (vector, camera) {

            console.warn('THREE.Projector: .unprojectVector() is now vector.unproject().');
            vector.unproject(camera);

        };

        this.pickingRay = function (vector, camera) {

            console.error('THREE.Projector: .pickingRay() is now raycaster.setFromCamera().');

        };

        //

        var RenderList = function () {

            var normals = [];
            var uvs = [];

            var object = null;
            var material = null;

            var normalMatrix = new THREE.Matrix3();

            var setObject = function (value) {

                object = value;
                material = object.material;

                normalMatrix.getNormalMatrix(object.matrixWorld);

                normals.length = 0;
                uvs.length = 0;

            };

            var projectVertex = function (vertex) {

                var position = vertex.position;
                var positionWorld = vertex.positionWorld;
                var positionScreen = vertex.positionScreen;

                positionWorld.copy(position).applyMatrix4(_modelMatrix);
                positionScreen.copy(positionWorld).applyMatrix4(_viewProjectionMatrix);

                var invW = 1 / positionScreen.w;

                positionScreen.x *= invW;
                positionScreen.y *= invW;
                positionScreen.z *= invW;

                vertex.visible = positionScreen.x >= -1 && positionScreen.x <= 1 &&
                    positionScreen.y >= -1 && positionScreen.y <= 1 &&
                    positionScreen.z >= -1 && positionScreen.z <= 1;

            };

            var pushVertex = function (x, y, z) {

                _vertex = getNextVertexInPool();
                _vertex.position.set(x, y, z);

                projectVertex(_vertex);

            };

            var pushNormal = function (x, y, z) {

                normals.push(x, y, z);

            };

            var pushUv = function (x, y) {

                uvs.push(x, y);

            };

            var checkTriangleVisibility = function (v1, v2, v3) {

                if (v1.visible === true || v2.visible === true || v3.visible === true) return true;

                _points3[0] = v1.positionScreen;
                _points3[1] = v2.positionScreen;
                _points3[2] = v3.positionScreen;

                return _clipBox.isIntersectionBox(_boundingBox.setFromPoints(_points3));

            };

            var checkBackfaceCulling = function (v1, v2, v3) {

                return ( ( v3.positionScreen.x - v1.positionScreen.x ) *
                    ( v2.positionScreen.y - v1.positionScreen.y ) -
                    ( v3.positionScreen.y - v1.positionScreen.y ) *
                    ( v2.positionScreen.x - v1.positionScreen.x ) ) < 0;

            };

            var pushLine = function (a, b) {

                var v1 = _vertexPool[a];
                var v2 = _vertexPool[b];

                _line = getNextLineInPool();

                _line.id = object.id;
                _line.v1.copy(v1);
                _line.v2.copy(v2);
                _line.z = ( v1.positionScreen.z + v2.positionScreen.z ) / 2;
                _line.renderOrder = object.renderOrder;

                _line.material = object.material;

                _renderData.elements.push(_line);

            };

            var pushTriangle = function (a, b, c) {

                var v1 = _vertexPool[a];
                var v2 = _vertexPool[b];
                var v3 = _vertexPool[c];

                if (checkTriangleVisibility(v1, v2, v3) === false) return;

                if (material.side === THREE.DoubleSide || checkBackfaceCulling(v1, v2, v3) === true) {

                    _face = getNextFaceInPool();

                    _face.id = object.id;
                    _face.v1.copy(v1);
                    _face.v2.copy(v2);
                    _face.v3.copy(v3);
                    _face.z = ( v1.positionScreen.z + v2.positionScreen.z + v3.positionScreen.z ) / 3;
                    _face.renderOrder = object.renderOrder;

                    // use first vertex normal as face normal

                    _face.normalModel.fromArray(normals, a * 3);
                    _face.normalModel.applyMatrix3(normalMatrix).normalize();

                    for (var i = 0; i < 3; i++) {

                        var normal = _face.vertexNormalsModel[i];
                        normal.fromArray(normals, arguments[i] * 3);
                        normal.applyMatrix3(normalMatrix).normalize();

                        var uv = _face.uvs[i];
                        uv.fromArray(uvs, arguments[i] * 2);

                    }

                    _face.vertexNormalsLength = 3;

                    _face.material = object.material;

                    _renderData.elements.push(_face);

                }

            };

            return {
                setObject: setObject,
                projectVertex: projectVertex,
                checkTriangleVisibility: checkTriangleVisibility,
                checkBackfaceCulling: checkBackfaceCulling,
                pushVertex: pushVertex,
                pushNormal: pushNormal,
                pushUv: pushUv,
                pushLine: pushLine,
                pushTriangle: pushTriangle
            }

        };

        var renderList = new RenderList();

        this.projectScene = function (scene, camera, sortObjects, sortElements) {

            _faceCount = 0;
            _lineCount = 0;
            _spriteCount = 0;

            _renderData.elements.length = 0;

            if (scene.autoUpdate === true) scene.updateMatrixWorld();
            if (camera.parent === null) camera.updateMatrixWorld();

            _viewMatrix.copy(camera.matrixWorldInverse.getInverse(camera.matrixWorld));
            _viewProjectionMatrix.multiplyMatrices(camera.projectionMatrix, _viewMatrix);

            _frustum.setFromMatrix(_viewProjectionMatrix);

            //

            _objectCount = 0;

            _renderData.objects.length = 0;
            _renderData.lights.length = 0;

            scene.traverseVisible(function (object) {

                if (object instanceof THREE.Light) {

                    _renderData.lights.push(object);

                } else if (object instanceof THREE.Mesh || object instanceof THREE.Line || object instanceof THREE.Sprite) {

                    var material = object.material;

                    if (material.visible === false) return;

                    if (object.frustumCulled === false || _frustum.intersectsObject(object) === true) {

                        _object = getNextObjectInPool();
                        _object.id = object.id;
                        _object.object = object;

                        _vector3.setFromMatrixPosition(object.matrixWorld);
                        _vector3.applyProjection(_viewProjectionMatrix);
                        _object.z = _vector3.z;
                        _object.renderOrder = object.renderOrder;

                        _renderData.objects.push(_object);

                    }

                }

            });

            if (sortObjects === true) {

                _renderData.objects.sort(painterSort);

            }

            //

            for (var o = 0, ol = _renderData.objects.length; o < ol; o++) {

                var object = _renderData.objects[o].object;
                var geometry = object.geometry;

                renderList.setObject(object);

                _modelMatrix = object.matrixWorld;

                _vertexCount = 0;

                if (object instanceof THREE.Mesh) {

                    if (geometry instanceof THREE.BufferGeometry) {

                        var attributes = geometry.attributes;
                        var groups = geometry.groups;

                        if (attributes.position === undefined) continue;

                        var positions = attributes.position.array;

                        for (var i = 0, l = positions.length; i < l; i += 3) {

                            renderList.pushVertex(positions[i], positions[i + 1], positions[i + 2]);

                        }

                        if (attributes.normal !== undefined) {

                            var normals = attributes.normal.array;

                            for (var i = 0, l = normals.length; i < l; i += 3) {

                                renderList.pushNormal(normals[i], normals[i + 1], normals[i + 2]);

                            }

                        }

                        if (attributes.uv !== undefined) {

                            var uvs = attributes.uv.array;

                            for (var i = 0, l = uvs.length; i < l; i += 2) {

                                renderList.pushUv(uvs[i], uvs[i + 1]);

                            }

                        }

                        if (geometry.index !== null) {

                            var indices = geometry.index.array;

                            if (groups.length > 0) {

                                for (var o = 0; o < groups.length; o++) {

                                    var group = groups[o];

                                    for (var i = group.start, l = group.start + group.count; i < l; i += 3) {

                                        renderList.pushTriangle(indices[i], indices[i + 1], indices[i + 2]);

                                    }

                                }

                            } else {

                                for (var i = 0, l = indices.length; i < l; i += 3) {

                                    renderList.pushTriangle(indices[i], indices[i + 1], indices[i + 2]);

                                }

                            }

                        } else {

                            for (var i = 0, l = positions.length / 3; i < l; i += 3) {

                                renderList.pushTriangle(i, i + 1, i + 2);

                            }

                        }

                    } else if (geometry instanceof THREE.Geometry) {

                        var vertices = geometry.vertices;
                        var faces = geometry.faces;
                        var faceVertexUvs = geometry.faceVertexUvs[0];

                        _normalMatrix.getNormalMatrix(_modelMatrix);

                        var material = object.material;

                        var isFaceMaterial = material instanceof THREE.MeshFaceMaterial;
                        var objectMaterials = isFaceMaterial === true ? object.material : null;

                        for (var v = 0, vl = vertices.length; v < vl; v++) {

                            var vertex = vertices[v];

                            _vector3.copy(vertex);

                            if (material.morphTargets === true) {

                                var morphTargets = geometry.morphTargets;
                                var morphInfluences = object.morphTargetInfluences;

                                for (var t = 0, tl = morphTargets.length; t < tl; t++) {

                                    var influence = morphInfluences[t];

                                    if (influence === 0) continue;

                                    var target = morphTargets[t];
                                    var targetVertex = target.vertices[v];

                                    _vector3.x += ( targetVertex.x - vertex.x ) * influence;
                                    _vector3.y += ( targetVertex.y - vertex.y ) * influence;
                                    _vector3.z += ( targetVertex.z - vertex.z ) * influence;

                                }

                            }

                            renderList.pushVertex(_vector3.x, _vector3.y, _vector3.z);

                        }

                        for (var f = 0, fl = faces.length; f < fl; f++) {

                            var face = faces[f];

                            material = isFaceMaterial === true
                                ? objectMaterials.materials[face.materialIndex]
                                : object.material;

                            if (material === undefined) continue;

                            var side = material.side;

                            var v1 = _vertexPool[face.a];
                            var v2 = _vertexPool[face.b];
                            var v3 = _vertexPool[face.c];

                            if (renderList.checkTriangleVisibility(v1, v2, v3) === false) continue;

                            var visible = renderList.checkBackfaceCulling(v1, v2, v3);

                            if (side !== THREE.DoubleSide) {

                                if (side === THREE.FrontSide && visible === false) continue;
                                if (side === THREE.BackSide && visible === true) continue;

                            }

                            _face = getNextFaceInPool();

                            _face.id = object.id;
                            _face.v1.copy(v1);
                            _face.v2.copy(v2);
                            _face.v3.copy(v3);

                            _face.normalModel.copy(face.normal);

                            if (visible === false && ( side === THREE.BackSide || side === THREE.DoubleSide )) {

                                _face.normalModel.negate();

                            }

                            _face.normalModel.applyMatrix3(_normalMatrix).normalize();

                            var faceVertexNormals = face.vertexNormals;

                            for (var n = 0, nl = Math.min(faceVertexNormals.length, 3); n < nl; n++) {

                                var normalModel = _face.vertexNormalsModel[n];
                                normalModel.copy(faceVertexNormals[n]);

                                if (visible === false && ( side === THREE.BackSide || side === THREE.DoubleSide )) {

                                    normalModel.negate();

                                }

                                normalModel.applyMatrix3(_normalMatrix).normalize();

                            }

                            _face.vertexNormalsLength = faceVertexNormals.length;

                            var vertexUvs = faceVertexUvs[f];

                            if (vertexUvs !== undefined) {

                                for (var u = 0; u < 3; u++) {

                                    _face.uvs[u].copy(vertexUvs[u]);

                                }

                            }

                            _face.color = face.color;
                            _face.material = material;

                            _face.z = ( v1.positionScreen.z + v2.positionScreen.z + v3.positionScreen.z ) / 3;
                            _face.renderOrder = object.renderOrder;

                            _renderData.elements.push(_face);

                        }

                    }

                } else if (object instanceof THREE.Line) {

                    if (geometry instanceof THREE.BufferGeometry) {

                        var attributes = geometry.attributes;

                        if (attributes.position !== undefined) {

                            var positions = attributes.position.array;

                            for (var i = 0, l = positions.length; i < l; i += 3) {

                                renderList.pushVertex(positions[i], positions[i + 1], positions[i + 2]);

                            }

                            if (geometry.index !== null) {

                                var indices = geometry.index.array;

                                for (var i = 0, l = indices.length; i < l; i += 2) {

                                    renderList.pushLine(indices[i], indices[i + 1]);

                                }

                            } else {

                                var step = object instanceof THREE.LineSegments ? 2 : 1;

                                for (var i = 0, l = ( positions.length / 3 ) - 1; i < l; i += step) {

                                    renderList.pushLine(i, i + 1);

                                }

                            }

                        }

                    } else if (geometry instanceof THREE.Geometry) {

                        _modelViewProjectionMatrix.multiplyMatrices(_viewProjectionMatrix, _modelMatrix);

                        var vertices = object.geometry.vertices;

                        if (vertices.length === 0) continue;

                        v1 = getNextVertexInPool();
                        v1.positionScreen.copy(vertices[0]).applyMatrix4(_modelViewProjectionMatrix);

                        var step = object instanceof THREE.LineSegments ? 2 : 1;

                        for (var v = 1, vl = vertices.length; v < vl; v++) {

                            v1 = getNextVertexInPool();
                            v1.positionScreen.copy(vertices[v]).applyMatrix4(_modelViewProjectionMatrix);

                            if (( v + 1 ) % step > 0) continue;

                            v2 = _vertexPool[_vertexCount - 2];

                            _clippedVertex1PositionScreen.copy(v1.positionScreen);
                            _clippedVertex2PositionScreen.copy(v2.positionScreen);

                            if (clipLine(_clippedVertex1PositionScreen, _clippedVertex2PositionScreen) === true) {

                                // Perform the perspective divide
                                _clippedVertex1PositionScreen.multiplyScalar(1 / _clippedVertex1PositionScreen.w);
                                _clippedVertex2PositionScreen.multiplyScalar(1 / _clippedVertex2PositionScreen.w);

                                _line = getNextLineInPool();

                                _line.id = object.id;
                                _line.v1.positionScreen.copy(_clippedVertex1PositionScreen);
                                _line.v2.positionScreen.copy(_clippedVertex2PositionScreen);

                                _line.z = Math.max(_clippedVertex1PositionScreen.z, _clippedVertex2PositionScreen.z);
                                _line.renderOrder = object.renderOrder;

                                _line.material = object.material;

                                if (object.material.vertexColors === THREE.VertexColors) {

                                    _line.vertexColors[0].copy(object.geometry.colors[v]);
                                    _line.vertexColors[1].copy(object.geometry.colors[v - 1]);

                                }

                                _renderData.elements.push(_line);

                            }

                        }

                    }

                } else if (object instanceof THREE.Sprite) {

                    _vector4.set(_modelMatrix.elements[12], _modelMatrix.elements[13], _modelMatrix.elements[14], 1);
                    _vector4.applyMatrix4(_viewProjectionMatrix);

                    var invW = 1 / _vector4.w;

                    _vector4.z *= invW;

                    if (_vector4.z >= -1 && _vector4.z <= 1) {

                        _sprite = getNextSpriteInPool();
                        _sprite.id = object.id;
                        _sprite.x = _vector4.x * invW;
                        _sprite.y = _vector4.y * invW;
                        _sprite.z = _vector4.z;
                        _sprite.renderOrder = object.renderOrder;
                        _sprite.object = object;

                        _sprite.rotation = object.rotation;

                        _sprite.scale.x = object.scale.x * Math.abs(_sprite.x - ( _vector4.x + camera.projectionMatrix.elements[0] ) / ( _vector4.w + camera.projectionMatrix.elements[12] ));
                        _sprite.scale.y = object.scale.y * Math.abs(_sprite.y - ( _vector4.y + camera.projectionMatrix.elements[5] ) / ( _vector4.w + camera.projectionMatrix.elements[13] ));

                        _sprite.material = object.material;

                        _renderData.elements.push(_sprite);

                    }

                }

            }

            if (sortElements === true) {

                _renderData.elements.sort(painterSort);

            }

            return _renderData;

        };

        // Pools

        function getNextObjectInPool() {

            if (_objectCount === _objectPoolLength) {

                var object = new THREE.RenderableObject();
                _objectPool.push(object);
                _objectPoolLength++;
                _objectCount++;
                return object;

            }

            return _objectPool[_objectCount++];

        }

        function getNextVertexInPool() {

            if (_vertexCount === _vertexPoolLength) {

                var vertex = new THREE.RenderableVertex();
                _vertexPool.push(vertex);
                _vertexPoolLength++;
                _vertexCount++;
                return vertex;

            }

            return _vertexPool[_vertexCount++];

        }

        function getNextFaceInPool() {

            if (_faceCount === _facePoolLength) {

                var face = new THREE.RenderableFace();
                _facePool.push(face);
                _facePoolLength++;
                _faceCount++;
                return face;

            }

            return _facePool[_faceCount++];


        }

        function getNextLineInPool() {

            if (_lineCount === _linePoolLength) {

                var line = new THREE.RenderableLine();
                _linePool.push(line);
                _linePoolLength++;
                _lineCount++;
                return line;

            }

            return _linePool[_lineCount++];

        }

        function getNextSpriteInPool() {

            if (_spriteCount === _spritePoolLength) {

                var sprite = new THREE.RenderableSprite();
                _spritePool.push(sprite);
                _spritePoolLength++;
                _spriteCount++;
                return sprite;

            }

            return _spritePool[_spriteCount++];

        }

        //

        function painterSort(a, b) {

            if (a.renderOrder !== b.renderOrder) {

                return a.renderOrder - b.renderOrder;

            } else if (a.z !== b.z) {

                return b.z - a.z;

            } else if (a.id !== b.id) {

                return a.id - b.id;

            } else {

                return 0;

            }

        }

        function clipLine(s1, s2) {

            var alpha1 = 0, alpha2 = 1,

            // Calculate the boundary coordinate of each vertex for the near and far clip planes,
            // Z = -1 and Z = +1, respectively.
                bc1near = s1.z + s1.w,
                bc2near = s2.z + s2.w,
                bc1far = -s1.z + s1.w,
                bc2far = -s2.z + s2.w;

            if (bc1near >= 0 && bc2near >= 0 && bc1far >= 0 && bc2far >= 0) {

                // Both vertices lie entirely within all clip planes.
                return true;

            } else if (( bc1near < 0 && bc2near < 0 ) || ( bc1far < 0 && bc2far < 0 )) {

                // Both vertices lie entirely outside one of the clip planes.
                return false;

            } else {

                // The line segment spans at least one clip plane.

                if (bc1near < 0) {

                    // v1 lies outside the near plane, v2 inside
                    alpha1 = Math.max(alpha1, bc1near / ( bc1near - bc2near ));

                } else if (bc2near < 0) {

                    // v2 lies outside the near plane, v1 inside
                    alpha2 = Math.min(alpha2, bc1near / ( bc1near - bc2near ));

                }

                if (bc1far < 0) {

                    // v1 lies outside the far plane, v2 inside
                    alpha1 = Math.max(alpha1, bc1far / ( bc1far - bc2far ));

                } else if (bc2far < 0) {

                    // v2 lies outside the far plane, v2 inside
                    alpha2 = Math.min(alpha2, bc1far / ( bc1far - bc2far ));

                }

                if (alpha2 < alpha1) {

                    // The line segment spans two boundaries, but is outside both of them.
                    // (This can't happen when we're only clipping against just near/far but good
                    //  to leave the check here for future usage if other clip planes are added.)
                    return false;

                } else {

                    // Update the s1 and s2 vertices to match the clipped line segment.
                    s1.lerp(s2, alpha1);
                    s2.lerp(s1, 1 - alpha2);

                    return true;

                }

            }

        }

    };
});